0.5mg Wegovy compared to Mounjaro: dose, strength and what patients often get wrong

The myth: 0.5mg is a like-for-like dose you can map across both medicines

The biggest misconception people bring to this comparison is that milligrams translate between Wegovy and Mounjaro the way they might between two versions of the same medicine. They don't. Semaglutide (Wegovy) and tirzepatide (Mounjaro) are structurally different drugs acting on different receptors. Wegovy targets the GLP-1 receptor; Mounjaro activates both GIP and GLP-1 receptors simultaneously, making it the only dual-agonist weight-loss medicine currently licensed in the UK. Comparing 0.5mg of one to any dose of the other is a bit like asking whether a 500mg paracetamol tablet is stronger than a 10mg antihistamine, the figure alone tells you almost nothing useful without the context of what each drug does and what dose is therapeutic. If you want to understand how the dose scales stack up across the full titration range, the Mounjaro to Wegovy dose conversion guide goes through the clinical thinking in detail. The short version: 0.5mg is a stepping stone, not a destination.

Where 0.5mg sits on Wegovy's dose ladder

Wegovy's titration sequence runs from 0.25mg through 0.5mg, 1.0mg, 1.7mg to a maintenance dose of 2.4mg, with each step held for roughly four weeks under prescriber guidance. So 0.5mg is the second rung. At that point the body is still adjusting, gastrointestinal side effects (nausea, loose stools, reflux) are most likely to be present, and meaningful weight loss is not yet the primary purpose of the dose. The overview of Wegovy doses compared to Mounjaro explains why this matters when people try to draw equivalence at any single point in the schedule. Mounjaro runs its own separate ladder: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, up to 15mg, as described in the Mounjaro and Wegovy cost comparison. Both ladders share the same logic (start low to reduce early side effects, then move up as the body settles) but the intervals, the numbers, and the endpoints are not interchangeable.

The full Wegovy vs Mounjaro comparison covers the broader picture if you're at the start of the decision rather than part-way through titration.

What the trial evidence says about outcomes

Comparing trial results across two separate drug programmes is inherently imperfect (the populations, endpoints and trial durations differed) but the headline figures from two landmark studies give useful context. In the STEP 1 trial (68 weeks, adults with obesity without diabetes), semaglutide 2.4mg produced an average body-weight reduction of around 15%, as published in the New England Journal of Medicine. Tirzepatide at 15mg in the SURMOUNT-1 trial produced average reductions of around 20–21% over 72 weeks, a finding that fed directly into NICE's appraisal of tirzepatide (TA1026). The SURMOUNT-5 head-to-head trial (published in NEJM 2025) confirmed that tirzepatide produced greater average weight reduction than semaglutide 2.4mg over 72 weeks in adults with obesity without diabetes. None of that evidence involves 0.5mg, it involves maintenance doses that patients typically reach after several months of careful titration. Outcomes at 0.5mg specifically are not meaningfully comparable to any Mounjaro maintenance dose; the question only becomes relevant once you understand where each medicine's therapeutic range sits, and our guide on 1mg Wegovy compared to Mounjaro shows how that picture begins to shift as you move up Wegovy's ladder. A clean summary of how the highest doses relate is in the 15mg Mounjaro and Wegovy equivalence guide.

Side effects and what patients at the 0.5mg step tend to notice

At 0.5mg semaglutide, the side-effect pattern is consistent with what the NHS documents for GLP-1 medicines generally: nausea is the most commonly reported complaint, alongside loose stools, indigestion, fatigue and the occasional headache. Symptoms tend to be most noticeable in the first week or two after a dose step, then settle. Mounjaro carries a broadly similar GI profile (nausea, vomiting, diarrhoea, constipation) because slowing gastric emptying is central to how both medicines work, regardless of receptor pathway. The NHS medicines page for semaglutide sets out the full side-effect list for Wegovy. For any side effect that is severe, persistent, or worrying (including stomach pain that spreads to the back, which can signal pancreatitis and needs urgent attention) speak to a clinician the same day rather than waiting for a review appointment. Our prescribers are available for aftercare seven days a week; our clinical team's approach is outlined on the clinical team page.

Which of these medicines is right for you is a clinical decision our prescribers make with you, based on your health history, current BMI, any existing conditions, and how you've responded to treatment before. To explore both options with a real clinician, start your free consultation.